NL8302903A - ANTENNA ACCORDING TO THE CASSEGRAIN PRINCIPLE WITH A SUPPORT FOR THE SUB-REFLECTOR. - Google Patents

Description

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Antenna according to the Cassegrain principle with a support for the sub-reflector.

The invention relates to an antenna according to the Cassegrain principle with a primary radiator and in particular a waveguide radiator, as well as a support for the sub-reflector.

In principle, such antennas are designed in the manner shown in Fig. 1.

With such antennas the problem exists to support the sub-reflector as much as possible without influencing the intermediate region HS between the horn radiator 1 and the sub-reflector 3 in the main reflector.

In known devices this is done by means of rods consisting of metal and plastic, as well as by means of self-supporting plastic caps, whereby a reduction of the radiation properties is taken for sale by the support construction. Also expensive multi-layer screws are used, which are the defined distances of the individual layers (depending on the operating wave length) partially compensate for the disturbing influence. However, this compensation is not only very expensive, but also only relatively narrow-banded, for example with a hand width of 10¾.

The object of the invention is to provide a support construction which, at low costs for the support construction, provides good electrical properties with regard to appearance.

The stated object is achieved with an antenna of the above-mentioned type according to the invention in that the sub-30 reflector is attached to the primary radiator by means of a tulip-shaped, solid body of hard foam plastic with a thin plastic coating, which is on the one hand near the the front of the primary radiator, which is preferably made of a horn, is affixed to the radiator 35 with the tulip bottom, and on the other hand is adhered at least at the edge of the sub-reflector at the opening of the tulip.

Advantageous further embodiments of the antenna according to the invention are described in the subclaims.

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This method of attaching the sub-reflector to the primary radiator has the advantage over the above antenna constructions that good electrical properties are obtained at low support costs. The proposed fastening construction does not contain any expensive compensation layers and operates essentially without dielectric waveguide according to the principle of the least possible field change due to the support construction.

The invention is explained in more detail below with reference to Figures 2 and 3.

Fig. 2 shows the principle of attaching the sub-reflector to the primary radiator.

Fig. 3 shows a complete exemplary embodiment, in which the part around the sub-reflector is shown partly cut-out.

The primary radiator 1 is connected to the sub-reflector 3 in the region HS according to Fig. 1 by means of a plastic body 2. In principle, this plastic body 2 has an approximately tulip-shaped shape. For the attachment of this plastic body 2 to the primary radiator 1, the latter is provided, in the illustrated exemplary embodiment, at the location indicated by 7 with a turned part, to which the plastic body is anchored by means of adhesive. The plastic body 25 is glued to the sub-reflector at the front end in particular at the outer edge. The plastic body consists of a hard foam plastic material with the least possible dielectric constant of, for example, ε ^ / ^ 1.05 and a loss factor of tang <s = 0.6. 10 “^. Such plastics with at least these properties are commercially available. In contrast to most commercially available plastics, the foam plastic is dimensionally stable up to a temperature of 180 ° C. The above-mentioned properties also apply to the range of very high frequencies, in particular, for example, about 15 GHz.

Particularly when the plastic body 2, as shown, is designed as a kind of truncated cone, a sufficiently great mechanical stability and strength are obtained despite the relatively low strength of the foamed plastic. In this respect, account must be taken of the fact that the supporting structure is subject to mechanical loads, such as impact loads, as well as to influences of varying ambient temperature, atmospheric loads, etc. ultraviolet rays and the like are exposed. However, it has been found that the material also has a sufficiently high durability in this respect.

In order to protect the plastic body on the one hand and to seal it on the other, it is advantageous to provide it with an outer covering consisting of plastic, as indicated by the dashed-dotted line 6. This outer covering consisting of plastic may consist of a layer of a hardening plastic, such as, for example, a polyester layer, which has been retrofitted around the whole and in the simplest case formed by a lacquer processing. Also a small thickness of this layer of, for instance, only 0.2 mm not only increases the stability of the hard foam plastic, but above all also seals it against the usually prevailing internal overpressure in the feed system. It is not necessary to compensate this protective layer additionally. This achieves an electrical behavior of the support construction, which corresponds to that of a roof construction with a wall thickness of 0.2 mm which is not practicable as such.

In order to influence the inevitable flare of the wave generated by the feeding horn radiator on the sub-reflector in phase, the shape of the supporting body is chosen as favorably as possible. For this latter purpose, the plastic body 2 is provided with at least one kink on the outside. However, it may be advantageous to arrange several kinks at this location. Therefore, the angle attenuation in the radiation diagram can be increased in the range from 30 to 90 °.

Furthermore, it is expedient to have a reinforcing collar 4 of a hard plastic, such as e.g.

Makrolon which extends over a defined distance over the tubular support of the primary radiator, which generally consists of a horn radiator. It is also expedient to allow the plastic body to protrude slightly beyond the edge of the sub-reflector, so that an adhesive joint 8 is created. On the other hand, it is not necessary to glue the plastic body over the entire surface of the sub-reflector with 87 Λ λ λ -r '3 b -J' J Ö% - 4 - or to let it rest against this surface. It is effective even for reasons of manufacturing technique and radiation properties to separate one between the sub-reflector and the plastic body. gradually widening rotationally symmetrical gap 9 from the periphery of the sub-reflector 5 towards the center thereof.

Fig. 3 shows the radiator again in its ultimate design, the plastic coating extending over the entire outer surface of the radiator and the sub-reflector, as well as the plastic body. The sub-reflector is hereby provided with tuning members covered by a hood on the front, as they are known per se.

The protective layer can be designed as a lacquer layer, as a single plastic-fiber-reinforced plastic layer or as a layer of other fibrous plastics. This layer increases the overall stability and impact strength of the surface and, when the antenna is connected to a compressed air fed waveguide, seals the drying air.

The air-permeable foam is also included in the dry air system.

The proposed solution constitutes an optimal combination of materials, which individually do not allow a satisfactory solution to the problem posed, but in the combination described above together with the high requirements with regard to the electrical behavior, the mechanical strength and the pressure density, as well as the influence of temperature and atmospheric load.

An important advantage of the described embodiment consists in that it avoids the manufacturing tolerances which are difficult to maintain in manufacturing terms, so that it is ensured that, even when serial production of these Cassegrain antennas, all units accurately meet the high requirements specified for that purpose. This applies in particular to the use of the antenna in highly concentrated systems for directional radio communications, in which a low secondary radiation, good reflection properties and a high degree of cross-polarization decoupling are required.

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Claims (7)

Antenna according to the Cassegrain principle with a primary radiator and in particular a waveguide radiator, and a support for the sub-reflector, characterized in that the sub-reflector (3) is attached to the primary radiator 5 (1X by means of a tulip-shaped solid body (2) of rigid foam plastic with a thin plastic coating, which is affixed to the radiator near the front of the primary radiator, preferably consisting of a horn radiator (1), with its tulip bodera and, on the other hand, at the location of the opening of the tulip is adhesively connected to at least the edge portion of the sub-reflector (3). Antenna according to claim 1, characterized in that the hard foam plastic (2) has the smallest possible relative dielectric constant (ε 1, 1.05) and a -4 r 15 small loss factor (tg δ <0.6 .. 10) at the operating frequency, as well as high dimensional stability up to higher temperatures (> 150 ° C). Antenna according to claim 1 or 2, characterized in that the tulip-shaped plastic body (2) is formed in the form of a cylindrical hollow truncated cone (3) in the middle corresponding to the opening diameter of the radiator, of which the cut-off top portion is connected to the front portion of the radiator (1) and the base surface of which is located near the periphery of the sub-reflector and at least 25 in its peripheral portion is adapted to this periphery and is in this connection connected to the sub-reflector. Antenna according to claim 3, characterized in that the plastic body has an outer circumferential shape, which is first cylindrical and then conical, ie conical, from the sub-reflector (3). 5. Antenna according to claim 4, characterized in that the transition between the conical and the cylindrical portion of the outer jacket is multi-stepped. Antenna according to one of the preceding claims, characterized in that the plastic body (2) is located. at the location of the radiator extends over the preferably stepped (7) outer circumference thereof and at this location is provided with an additional reinforcing sleeve (4) which extends over a further part of the outer circumference of the radiator. 40.s / L i öSO - 6 - - ς Antenna according to any one of the preceding claims, characterized in that the connections between the plastic body (2) and the radiator (1) on the one hand and the sub-reflector (3) on the other hand consist of adhesive connections. 5 ^ ffT Λ ^ A Λ * 7: - / f-ΐ, i i "; j kj 'J J'